1. Field of the Invention
This invention relates generally to semiconductor fabrication and, more particularly, to forming titanium nitride films.
2. Description of the Related Art
For various reasons, including low electrical resistivity, good thermal stability and good diffusion barrier properties, there are numerous applications for titanium nitride (TiN) in the fabrication of integrated circuits. Exemplary applications include use as a contact or barrier layer and as an electrode in electrical devices, such as transistors.
The properties of TiN, however, are closely dependent on processing and deposition parameters. Thus, the suitability and desirability of deposited TiN for a particular application can depend on the availability of a deposition process able to form TiN with desired properties, e.g., high uniformity and low resistivity. As a result, research into the development of new TiN deposition processes is on-going.
For example, the Low Pressure Chemical Vapor Deposition (LPCVD) of TiN films in a hot wall furnace has recently been described by N. Ramanuja et al. in Materials Letters, Vol. 57 (2002), pp. 261-269. The reach of Ramanuja et al. is limited, however, as Ramanuja et al. investigated 100 mm wafers, rather than industry standard 200 mm and 300 mm wafers. Given the sensitivity of TiN films to deposition conditions, a need still remains for a process that is able to deposit TiN films with good uniformity and low resistivity on industry size wafers, such as 200 mm or 300 mm wafers.
In addition to being able to form acceptable TiN films, it is desirable for the deposition temperature of the TiN deposition process to be relatively low, thereby increasing flexibility for integrating the deposition process with other processes and structures. For example, reducing deposition temperatures to the 400-500° C. range would allow the films to be used in conjunction with multi-level aluminum or copper metallization.
It has been found, however, that a reduction in the deposition temperature results in the incorporation of significant amounts of chlorine in the TiN film and results in a substantial increase in resistivity, which is undesirable. See J. T. Hillman, Microelectronic Engineering, Vol. 19 (1992), pp. 375-378. To reduce the resistivity and the chlorine content of the film, Hilman discloses a single wafer deposition process followed by a post-deposition anneal. Undesirably, however, such a process requires an additional process step and also limits throughput by using single wafer processing.
Accordingly, there is a need for an economical, relatively high throughput process for depositing TiN films having good uniformity and low resistivity.